We regret for the inconvenience caused. We are unable to reproduce the issue in our end.We request you to check whether you have set Localize="en-US" in your aspx.cs and do check whether your resource file "GridGrouping.en-US.resx" is named correctly.

We have created a video demonstration,So could you please try to reproduce the issue in our sample and send us back or send your sample so that we can provide you a better solution?

[Default.aspx.cs]:

if (!IsPostBack)

{

List<MyClass1> list = new List<MyClass1>();

this.GridGroupingControl1.DataSource = list;

this.GridGroupingControl1.TableDescriptor.Localize ="en-US";

}

Please find the attached video below and let us know if you need further assistance.